U.S. patent number 10,072,206 [Application Number 15/197,891] was granted by the patent office on 2018-09-11 for processes for preparing color stable red-emitting phosphors.
This patent grant is currently assigned to General Electric Company. The grantee listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Fangming Du, James Edward Murphy, Anant Achyut Setlur.
United States Patent |
10,072,206 |
Murphy , et al. |
September 11, 2018 |
Processes for preparing color stable red-emitting phosphors
Abstract
Processes for preparing color stable red-emitting phosphors
include contacting a complex fluoride phosphor of formula I with a
first fluorine-containing oxidizing agent in gaseous form at a
first temperature ranging from 200.degree. C. to 700.degree. C. to
form a first product phosphor, contacting the first product
phosphor in particulate form with a solution of a compound of
formula II in aqueous hydrofluoric acid to form a treated phosphor,
and contacting the treated phosphor with a second
fluorine-containing oxidizing agent in gaseous form at a second
temperature <225.degree. C., A.sub.xMF.sub.y:MN.sup.4+ I
A.sub.xMF.sub.y II wherein A is independently at each occurrence
Li, Na, K, Rb, Cs or a combination thereof, M is independently at
each occurrence Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb,
Ta, Bi, Gd, or a combination thereof, x is absolute value of the
charge of the MF.sub.y ion; and y is 5, 6 or 7.
Inventors: |
Murphy; James Edward
(Niskayuna, NY), Du; Fangming (Hudson, OH), Setlur; Anant
Achyut (Niskayuna, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
60806559 |
Appl.
No.: |
15/197,891 |
Filed: |
June 30, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180002598 A1 |
Jan 4, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K
11/616 (20130101) |
Current International
Class: |
C09K
11/61 (20060101) |
Field of
Search: |
;252/301.4F,301.4H,301.4R,301.6F ;428/403 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Lepoutre et al., "Structural investigations of sol-gel-derived
LiYF4 and LiGdF4 powders", Journal of Solid State Chemistry, vol.
180, Issue: 11, pp. 3049-3057, Nov. 2007. cited by
applicant.
|
Primary Examiner: Hoban; Matthew E
Assistant Examiner: Edmondson; Lynne
Attorney, Agent or Firm: Winter; Catherine J.
Claims
The invention claimed is:
1. A process comprising contacting a complex fluoride phosphor of
formula I, A.sub.xMF.sub.y:MN.sup.4+ I with a first
fluorine-containing oxidizing agent in gaseous form at a first
temperature ranging from greater than 200.degree. C. to about
700.degree. C., to form a first product phosphor; contacting the
first product phosphor in particulate form with a solution of a
compound of formula II in aqueous hydrofluoric acid,
A.sub.xMF.sub.y II to form a treated phosphor; and contacting the
treated phosphor with a second fluorine-containing oxidizing agent
in gaseous form at a second temperature of less than 225.degree.
C.; wherein A is independently at each occurrence Li, Na, K, Rb,
Cs, or a combination thereof; M independently at each occurrence is
Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a
combination thereof; x is the absolute value of the charge of the
MF.sub.y ion; and y is 5, 6 or 7.
2. A process according to claim 1, wherein the first and second
fluorine-containing oxidizing agents are independently selected
from F.sub.2, HF, SF.sub.6, BrF.sub.5, NH.sub.4HF.sub.2, NH.sub.4F,
KF, AlF.sub.3, SbF.sub.5, ClF.sub.3, BrF.sub.3, KrF, XeF.sub.2,
XeF.sub.4, NF.sub.3, SiF.sub.4, PbF.sub.2, ZnF.sub.2, SnF.sub.2,
CdF.sub.2, C.sub.1-C.sub.4 fluorocarbons, and combinations
thereof.
3. A process according to claim 1, wherein each of the first and
second fluorine-containing oxidizing agent is F.sub.2.
4. A process according to claim 1, wherein M independently at each
occurrence is Si, Ge, Sn, Ti, Zr, or a combination thereof.
5. A process according to claim 1, wherein A independently at each
occurrence is Na, K, Rb, Cs, or a combination thereof; M
independently at each occurrence is Si, Ge, Ti, or a combination
thereof; and y is 6.
6. A process according to claim 1, wherein the complex fluoride
phosphor is K.sub.2SiF.sub.6:Mn.sup.4+.
7. A process according to claim 1, wherein the compound of formula
II is K.sub.2SiF.sub.6.
8. A process according to claim 1, wherein the first temperature is
any temperature in a range from about 350.degree. C. to about
700.degree. C.
9. A process according to claim 1, wherein the second temperature
is any temperature in a range less than 225.degree. C.
10. A process according to claim 1, wherein the second temperature
is any temperature in a range less than 100.degree. C.
11. A process according to claim 1, wherein the second temperature
is about 90.degree. C.
12. A process according to claim 1, wherein the treated phosphor is
contacted with the second fluorine-containing oxidizing agent for a
period of about eight hours.
13. A process according to claim 1, wherein the treated phosphor is
contacted with the second fluorine-containing oxidizing agent for a
period of about eight hours at a temperature of about 90.degree.
C.
14. A process according to claim 1, wherein the treated phosphor is
contained in a vessel having a non-metallic surface during contact
with the second fluorine-containing oxidizing agent.
15. A process according to claim 14, wherein the non-metallic
surface comprises a fluoropolymer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. patent application entitled
PROCESSES FOR PREPARING COLOR STABLE RED-EMITTING PHOSPHORS filed
concurrently herewith under Ser. No. 15/197,897
BACKGROUND
Red-emitting phosphors based on complex fluoride materials
activated by Mn.sup.4+, such as those described in U.S. Pat. Nos.
7,358,542, 7,497,973, and 7,648,649, can be utilized in combination
with yellow/green emitting phosphors such as YAG:Ce or other garnet
compositions to achieve warm white light (CCTs<5000 K on the
blackbody locus, color rendering index (CRI) >80) from a blue
LED, equivalent to that produced by current fluorescent,
incandescent and halogen lamps. These materials absorb blue light
strongly and efficiently emit between about 610-635 nm with little
deep red/NIR emission. Therefore, luminous efficacy is maximized
compared to red phosphors that have significant emission in the
deeper red where eye sensitivity is poor. Quantum efficiency can
exceed 85% under blue (440-460 nm) excitation.
One potential limitation in using Mn.sup.4+ doped fluoride hosts is
their susceptibility to degradation under high temperature and
humidity (HTHH) conditions. It is possible to reduce this
degradation using post-synthesis processing steps, as described in
U.S. Pat. Nos. 8,252,613, 8,710,487, 8,906,724, and other patent
applications assigned to General Electric Company. However, further
improvement in stability of the materials is desirable.
BRIEF DESCRIPTION
Briefly, in one aspect, the present invention relates to a process
that includes contacting a complex fluoride phosphor of formula I,
A.sub.xMF.sub.y:Mn.sup.4+ I with a first fluorine-containing
oxidizing agent in gaseous form at a first temperature ranging from
about 200.degree. C. to about 700.degree. C., to form a first
product phosphor; contacting the first product phosphor in
particulate form with a solution of a compound of formula II in
aqueous hydrofluoric acid, A.sub.xMF.sub.y II to form a treated
phosphor; and contacting the treated phosphor with a second
fluorine-containing oxidizing agent in gaseous form at a second
temperature of less than 225.degree. C.;
wherein A is independently at each occurrence Li, Na, K, Rb, Cs, or
a combination thereof; M is independently at each occurrence Si,
Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a
combination thereof; x is the absolute value of the charge of the
MF.sub.y ion; and y is 5, 6 or 7.
DRAWINGS
These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in
which like characters represent like parts throughout the drawings,
wherein:
FIG. 1 is a schematic cross-sectional view of a lighting apparatus
in accordance with one embodiment of the invention;
FIG. 2 is a schematic cross-sectional view of a lighting apparatus
in accordance with another embodiment of the invention;
FIG. 3 is a schematic cross-sectional view of a lighting apparatus
in accordance with yet another embodiment of the invention;
FIG. 4 is a cutaway side perspective view of a lighting apparatus
in accordance with one embodiment of the invention;
FIG. 5 is a schematic perspective view of a surface-mounted device
(SMD) backlight LED.
DETAILED DESCRIPTION
In the context of the present invention, the terms "complex
fluoride material" "complex fluoride phosphor" and "complex
fluoride compound" mean a coordination compound containing at least
one coordination center surrounded by fluoride ions acting as
ligands, and charge-compensated by counter ions as necessary. In
one example, K.sub.2SiF.sub.6:Mn.sup.4+, the coordination center is
Si and the counterion is K. Complex fluorides are occasionally
written as a combination of simple, binary fluorides but such a
representation does not indicate the coordination number for the
ligands around the coordination center. The square brackets
(occasionally omitted for simplicity) indicate that the complex ion
they encompass is a new chemical species, different from the simple
fluoride ion. The Mn.sup.4+ activator ion also acts as a
coordination center, substituting part of the centers of the host
lattice, for example, Si. The host lattice, including the counter
ions, may further modify the excitation and emission properties of
the activator ion.
The amount of manganese in the Mn.sup.4+ doped phosphors of formula
I ranges from about 1 mol % to about 30 mol %, particularly from
about 3 mol % to about 20 mol %. In embodiments where the phosphor
formula I is K.sub.2SiF.sub.6:Mn.sup.4+, the amount of manganese
ranges from about 1 mol % (about 0.25 wt %) to about 25 mol %
(about 6 wt %), particularly from about 2 mol % (about 0.5 wt %) to
about 20 mol (about 5 wt %), and more particularly from about 2 mol
% (about 0.5 wt %) to about 4 wt % (about 16.5 mol %).
In particular embodiments, the coordination center of the phosphor,
that is, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combination
thereof. More particularly, the coordination center is Si, Ge, Ti,
or a combination thereof, and the counterion, or A in formula I, is
Na, K, Rb, Cs, or a combination thereof, and y is 6. Examples of
phosphors of formula I include K.sub.2SiF.sub.6:Mn.sup.4+,
K.sub.2TiF.sub.6:Mn.sup.4+, K.sub.2SnF.sub.6:Mn.sup.4+,
Cs.sub.2TiF.sub.6, Rb.sub.2TiF.sub.6, Cs.sub.2SiF.sub.6,
Rb.sub.2SiF.sub.6, Na.sub.2TiFe:Mn.sup.4+, Na.sub.2ZrFe:Mn.sup.4+,
K.sub.3ZrF.sub.7:Mn.sup.4+, K.sub.3BiFe:Mn.sup.4+,
K.sub.3YFe:Mn.sup.4+, K.sub.3LaFe:Mn.sup.4+,
K.sub.3GdF.sub.6:Mn.sup.4+, K.sub.3NbF.sub.7:Mn.sup.4+,
K.sub.3TaF.sub.7:Mn.sup.4+. In particular embodiments, the phosphor
of formula I is K.sub.2SiFe:Mn.sup.4+
In some embodiments, the phosphor is selected from the group
consisting of (A) A.sub.2MF.sub.5:Mn.sup.4+, where A is selected
from Li, Na, K, Rb, Cs, and combinations thereof; and where M is
selected from Al, Ga, In, and combinations thereof; (B)
A.sub.3MFe:Mn.sup.4+, where A is selected from Li, Na, K, Rb, Cs,
and combinations thereof; and where M is selected from Al, Ga, In,
and combinations thereof; (C) Zn.sub.2MF.sub.7:Mn.sup.4+, where M
is selected from Al, Ga, In, and combinations thereof; (D)
Aln.sub.2F.sub.7:Mn.sup.4+ where A is selected from Li, Na, K, Rb,
Cs, and combinations thereof; (E) A.sub.2MFe:Mn.sup.4+, where A is
selected from Li, Na, K, Rb, Cs, and combinations thereof; and
where M is selected from Ge, Si, Sn, Ti, Zr, and combinations
thereof; (F) EMFe:Mn.sup.4+, where E is selected from Mg, Ca, Sr,
Ba, Zn, and combinations thereof; and where M is selected from Ge,
Si, Sn, Ti, Zr, and combinations thereof; (G)
Ba.sub.0.65Zr.sub.0.35F.sub.2.70:Mn.sup.4+; and (H)
A.sub.3ZrF.sub.7:Mn.sup.4+ where A is selected from Li, Na, K, Rb,
Cs, NH.sub.4; and combinations thereof.
Although the inventors do not wish to be held to any particular
theory to explain the improvement in color stability that can
result from subjecting the phosphor to a process according to the
present invention, it is postulated that the phosphor may contain
defects such as dislocations, F.sup.- vacancies, cation vacancies,
Mn.sup.3+ ions, Mn.sup.2+ ions, OH.sup.- replacement of F.sup.-, or
surface or interstitial H.sup.+/OH.sup.- groups that provide
non-radiative recombination pathways, and these are healed or
removed by exposure to the oxidizing agent at elevated
temperature.
In a first step of a process according to the present invention, a
complex fluoride phosphor of formula I is contacted with a first
fluorine-containing oxidizing agent in gaseous form at a first
temperature to form a first product phosphor. The first temperature
ranges from about 200.degree. C. to about 700.degree. C.,
particularly from about 350.degree. C. to about 700.degree. C.
during contact, and in some embodiments from about 500.degree. C.
to about 700.degree. C. The phosphor is contacted with the
oxidizing agent for a period of time sufficient to convert it to a
color stable phosphor. Time and temperature are interrelated, and
may be adjusted together, for example, increasing time while
reducing temperature, or increasing temperature while reducing
time. In particular embodiments, the time is at least one hour,
particularly for at least four hours, more particularly at least
six hours, and most particularly at least eight hours. In a
specific embodiment, the phosphor is contacted with the oxidizing
agent for a period of at least eight hours at a first temperature
of about 500.degree. C.
The fluorine-containing oxidizing agent may be F.sub.2, HF,
SF.sub.6, BrF.sub.5, NH.sub.4HF.sub.2, NH.sub.4F, KF, AlF.sub.3,
SbF.sub.5, ClF.sub.3, BrF.sub.3, KrF, XeF.sub.2, XeF.sub.4,
NF.sub.3, SiF.sub.4, PbF.sub.2, ZnF.sub.2, SnF.sub.2, CdF.sub.2, a
C.sub.1-C.sub.4 fluorocarbon, or a combination thereof. Examples of
suitable fluorocarbons include CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, CHF.sub.3, CF.sub.3CH.sub.2F, and CF.sub.2CHF. The
In particular embodiments, the fluorine-containing oxidizing agent
is F.sub.2. The amount of oxidizing agent in the atmosphere may be
varied to obtain the color stable phosphor, particularly in
conjunction with variation of time and temperature. Where the
fluorine-containing oxidizing agent is F.sub.2, the atmosphere may
include at least 0.5% F.sub.2, although a lower concentration may
be effective in some embodiments. In particular, the atmosphere may
include at least 5% F.sub.2 and more particularly at least 20%
F.sub.2. The atmosphere may additionally include nitrogen, helium,
neon, argon, krypton, xenon, in any combination with the
fluorine-containing oxidizing agent. In particular embodiments, the
atmosphere is composed of about 20% F.sub.2 and about 80%
nitrogen.
The manner of contacting the phosphor with the fluorine-containing
oxidizing agent is not critical and may be accomplished in any way
sufficient to yield a color stable phosphor having the desired
properties. In some embodiments, the chamber containing the
phosphor may be dosed and then sealed such that an overpressure
develops as the chamber is heated, and in others, the fluorine and
nitrogen mixture is flowed throughout the anneal process ensuring a
more uniform pressure. In some embodiments, an additional dose of
the fluorine-containing oxidizing agent may be introduced after a
period of time.
In a second step, the first product phosphor produced in the first
step is contacted with a solution of a compound of formula II in
aqueous hydrofluoric acid, A.sub.xMF.sub.y II to form a treated
phosphor, as described in U.S. Pat. Nos. 8,252,613, 8,710,487, and
US 2015/0054400. In preferred embodiments, the solution is
saturated or nearly saturated. A nearly saturated solution is one
that contains 1-10% solvent in excess of the amount required to
make a saturated solution. In one example,
K.sub.2SiF.sub.6:Mn.sup.4+ is treated with a nearly saturated
solution K.sub.2SiF.sub.6 in aqueous HF prepared by adding
approximately 1-5 vol % aqueous HF to a saturated solution of
K.sub.2SiF.sub.6 in aqueous HF.
The temperature at which the first product phosphor is contacted
with the solution is not particularly limited and may be selected
according to convenience, although other parameters such as time or
concentration may be adjusted at high or low temperatures to yield
the desired properties of the phosphor. In particular embodiments,
the temperature ranges from about 20.degree. C. to about 50.degree.
C. The period of time required to treat the phosphor ranges from
about one minute to about five hours, particularly from about five
minutes to about one hour. Concentration of hydrofluoric acid in
the aqueous HF solutions ranges from about 20% w/w to about 70%
w/w, particularly about 40% w/w to about 70% w/w. Less concentrated
solutions may result in lower yields of the phosphor.
In a third step, the treated phosphor is contacted with a second
fluorine-containing oxidizing agent in gaseous form at a second
temperature. The second temperature may the same as the first
temperature, or may be less than the it, ranging up to and
including 225.degree. C., particularly up to and including
100.degree. C., and more particularly, up to and including
90.degree. C. The time for contacting with the oxidizing agent in
the third step may be the same as the time for the first step. In
particular embodiments, the time is at least one hour, particularly
for at least four hours, more particularly at least six hours, and
most particularly at least eight hours. In a specific embodiment,
the phosphor is contacted with the oxidizing agent for a period of
at least eight hours at a temperature of about 90.degree. C. The
oxidizing agent may be the same as or different from that used in
the first annealing step. In particular embodiments, the
fluorine-containing oxidizing agent is F.sub.2. More particularly,
the atmosphere may include at least 20% F.sub.2.
During the third step, the phosphor may be contained in a vessel
having a non-metallic surface in order to reduce contamination of
the phosphor with metals. In particular embodiments, the vessel and
surface thereof is composed of a fluoropolymer. For example, a
crucible or boat made of polytetrafluoroethylene may be used to
contain the phosphor. The resulting phosphor is dry and may have
fewer hydroxide groups on the surface of the particles. By reducing
surface groups such as hydroxides, the degree of agglomeration may
be reduced and correspondingly, decreased bulk density which may
result in an improvement in manufacturing.
A lighting apparatus or light emitting assembly or lamp 10
according to one embodiment of the present invention is shown in
FIG. 1. Lighting apparatus 10 includes a semiconductor radiation
source, shown as light emitting diode (LED) chip 12, and leads 14
electrically attached to the LED chip. The leads 14 may be thin
wires supported by a thicker lead frame(s) 16 or the leads may be
self supported electrodes and the lead frame may be omitted. The
leads 14 provide current to LED chip 12 and thus cause it to emit
radiation.
The lamp may include any semiconductor blue or UV light source that
is capable of producing white light when its emitted radiation is
directed onto the phosphor. In one embodiment, the semiconductor
light source is a blue emitting LED doped with various impurities.
Thus, the LED may comprise a semiconductor diode based on any
suitable III-V, II-VI or IV-IV semiconductor layers and having an
emission wavelength of about 250 to 550 nm. In particular, the LED
may contain at least one semiconductor layer comprising GaN, ZnSe
or SiC. For example, the LED may comprise a nitride compound
semiconductor represented by the formula In.sub.iGa.sub.jAl.sub.kN
(where 0.ltoreq.i; 0.ltoreq.j; 0.ltoreq.k and i+j+k=1) having an
emission wavelength greater than about 250 nm and less than about
550 nm. In particular embodiments, the chip is a near-uv or blue
emitting LED having a peak emission wavelength from about 400 to
about 500 nm. Such LED semiconductors are known in the art. The
radiation source is described herein as an LED for convenience.
However, as used herein, the term is meant to encompass all
semiconductor radiation sources including, e.g., semiconductor
laser diodes. Further, although the general discussion of the
exemplary structures of the invention discussed herein is directed
toward inorganic LED based light sources, it should be understood
that the LED chip may be replaced by another radiation source
unless otherwise noted and that any reference to semiconductor,
semiconductor LED, or LED chip is merely representative of any
appropriate radiation source, including, but not limited to,
organic light emitting diodes.
In lighting apparatus 10, phosphor composition 22 is radiationally
coupled to the LED chip 12. Radiationally coupled means that the
elements are associated with each other so radiation from one is
transmitted to the other. Phosphor composition 22 is deposited on
the LED 12 by any appropriate method. For example, a water based
suspension of the phosphor(s) can be formed, and applied as a
phosphor layer to the LED surface. In one such method, a silicone
slurry in which the phosphor particles are randomly suspended is
placed around the LED. This method is merely exemplary of possible
positions of phosphor composition 22 and LED 12. Thus, phosphor
composition 22 may be coated over or directly on the light emitting
surface of the LED chip 12 by coating and drying the phosphor
suspension over the LED chip 12. In the case of a silicone-based
suspension, the suspension is cured at an appropriate temperature.
Both the shell 18 and the encapsulant 20 should be transparent to
allow white light 24 to be transmitted through those elements.
Although not intended to be limiting, in some embodiments, the
median particle size of the phosphor composition ranges from about
1 to about 50 microns, particularly from about 15 to about 35
microns.
In other embodiments, phosphor composition 22 is interspersed
within the encapsulant material 20, instead of being formed
directly on the LED chip 12. The phosphor (in the form of a powder)
may be interspersed within a single region of the encapsulant
material 20 or throughout the entire volume of the encapsulant
material. Blue light emitted by the LED chip 12 mixes with the
light emitted by phosphor composition 22, and the mixed light
appears as white light. If the phosphor is to be interspersed
within the material of encapsulant 20, then a phosphor powder may
be added to a polymer or silicone precursor, loaded around the LED
chip 12, and then the polymer precursor may be cured to solidify
the polymer or silicone material. Other known phosphor
interspersion methods may also be used, such as transfer
loading.
In some embodiments, the encapsulant material 20 is a silicone
matrix having an index of refraction R, and, in addition to
phosphor composition 22, contains a diluent material having less
than about 5% absorbance and index of refraction of R.+-.0.1. The
diluent material has an index of refraction of .ltoreq.1.7,
particularly .ltoreq.1.6, and more particularly .ltoreq.1.5. In
particular embodiments, the diluent material is of formula II, and
has an index of refraction of about 1.4. Adding an optically
inactive material to the phosphor/silicone mixture may produce a
more gradual distribution of light flux through the
phosphor/encapsulant mixture and can result in less damage to the
phosphor. Suitable materials for the diluent include fluoride
compounds such as LiF, MgF.sub.2, CaF.sub.2, SrF.sub.2, AlF.sub.3,
K.sub.2NaAlF.sub.6, KMgF.sub.3, CaLiAlF.sub.6, K.sub.2LiAlF.sub.6,
and K.sub.2SiF.sub.6, which have index of refraction ranging from
about 1.38 (AlF.sub.3 and K.sub.2NaAlF.sub.6) to about 1.43
(CaF.sub.2), and polymers having index of refraction ranging from
about 1.254 to about 1.7. Non-limiting examples of polymers
suitable for use as a diluent include polycarbonates, polyesters,
nylons, polyetherimides, polyetherketones, and polymers derived
from styrene, acrylate, methacrylate, vinyl, vinyl acetate,
ethylene, propylene oxide, and ethylene oxide monomers, and
copolymers thereof, including halogenated and unhalogenated
derivatives. These polymer powders can be directly incorporated
into silicone encapsulants before silicone curing.
In yet another embodiment, phosphor composition 22 is coated onto a
surface of the shell 18, instead of being formed over the LED chip
12. The phosphor composition is preferably coated on the inside
surface of the shell 18, although the phosphor may be coated on the
outside surface of the shell, if desired. Phosphor composition 22
may be coated on the entire surface of the shell or only a top
portion of the surface of the shell. The UV/blue light emitted by
the LED chip 12 mixes with the light emitted by phosphor
composition 22, and the mixed light appears as white light. Of
course, the phosphor may be located in any two or all three
locations or in any other suitable location, such as separately
from the shell or integrated into the LED.
FIG. 2 illustrates a second structure of the system according to
the present invention. Corresponding numbers from FIGS. 1-4 (e.g.
12 in FIGS. 1 and 112 in FIG. 2) relate to corresponding structures
in each of the figures, unless otherwise stated. The structure of
the embodiment of FIG. 2 is similar to that of FIG. 1, except that
the phosphor composition 122 is interspersed within the encapsulant
material 120, instead of being formed directly on the LED chip 112.
The phosphor (in the form of a powder) may be interspersed within a
single region of the encapsulant material or throughout the entire
volume of the encapsulant material. Radiation (indicated by arrow
126) emitted by the LED chip 112 mixes with the light emitted by
the phosphor 122, and the mixed light appears as white light 124.
If the phosphor is to be interspersed within the encapsulant
material 120, then a phosphor powder may be added to a polymer
precursor, and loaded around the LED chip 112. The polymer or
silicone precursor may then be cured to solidify the polymer or
silicone. Other known phosphor interspersion methods may also be
used, such as transfer molding.
FIG. 3 illustrates a third possible structure of the system
according to the present invention. The structure of the embodiment
shown in FIG. 3 is similar to that of FIG. 1, except that the
phosphor composition 222 is coated onto a surface of the envelope
218, instead of being formed over the LED chip 212. The phosphor
composition 222 is preferably coated on the inside surface of the
envelope 218, although the phosphor may be coated on the outside
surface of the envelope, if desired. The phosphor composition 222
may be coated on the entire surface of the envelope, or only a top
portion of the surface of the envelope. The radiation 226 emitted
by the LED chip 212 mixes with the light emitted by the phosphor
composition 222, and the mixed light appears as white light 224. Of
course, the structures of FIGS. 1-3 may be combined, and the
phosphor may be located in any two or all three locations, or in
any other suitable location, such as separately from the envelope,
or integrated into the LED.
In any of the above structures, the lamp may also include a
plurality of scattering particles (not shown), which are embedded
in the encapsulant material. The scattering particles may comprise,
for example, alumina or titania. The scattering particles
effectively scatter the directional light emitted from the LED
chip, preferably with a negligible amount of absorption.
As shown in a fourth structure in FIG. 4, the LED chip 412 may be
mounted in a reflective cup 430. The cup 430 may be made from or
coated with a dielectric material, such as alumina, titania, or
other dielectric powders known in the art, or be coated by a
reflective metal, such as aluminum or silver. The remainder of the
structure of the embodiment of FIG. 4 is the same as those of any
of the previous figures, and can include two leads 416, a
conducting wire 432, and an encapsulant material 420. The
reflective cup 430 is supported by the first lead 416 and the
conducting wire 432 is used to electrically connect the LED chip
412 with the second lead 416.
Another structure (particularly for backlight applications) is a
surface mounted device ("SMD") type light emitting diode 550, e.g.
as illustrated in FIG. 5. This SMD is a "side-emitting type" and
has a light-emitting window 552 on a protruding portion of a light
guiding member 554. An SMD package may comprise an LED chip as
defined above, and a phosphor material that is excited by the light
emitted from the LED chip. Other backlight devices include, but are
not limited to, TVs, computers, smartphones, tablet computers and
other handheld devices that have a display including a
semiconductor light source; and a color stable Mn.sup.4+ doped
phosphor according to the present invention.
When used with an LED emitting at from 350 to 550 nm and one or
more other appropriate phosphors, the resulting lighting system
will produce a light having a white color. Lamp 10 may also include
scattering particles (not shown), which are embedded in the
encapsulant material. The scattering particles may comprise, for
example, alumina or titania. The scattering particles effectively
scatter the directional light emitted from the LED chip, preferably
with a negligible amount of absorption.
In addition to the color stable Mn.sup.4+ doped phosphor, phosphor
composition 22 may include one or more other phosphors. When used
in a lighting apparatus in combination with a blue or near UV LED
emitting radiation in the range of about 250 to 550 nm, the
resultant light emitted by the assembly will be a white light.
Other phosphors such as green, blue, yellow, red, orange, or other
color phosphors may be used in the blend to customize the white
color of the resulting light and produce specific spectral power
distributions. Other materials suitable for use in phosphor
composition 22 include electroluminescent polymers such as
polyfluorenes, preferably poly(9,9-dioctyl fluorene) and copolymers
thereof, such as
poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)diphenylamine)
(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and their
derivatives. In addition, the light emitting layer may include a
blue, yellow, orange, green or red phosphorescent dye or metal
complex, or a combination thereof. Materials suitable for use as
the phosphorescent dye include, but are not limited to,
tris(1-phenylisoquinoline) iridium (III) (red dye),
tris(2-phenylpyridine) iridium (green dye) and Iridium (III)
bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye). Commercially
available fluorescent and phosphorescent metal complexes from ADS
(American Dyes Source, Inc.) may also be used. ADS green dyes
include ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, and
ADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE.
ADS red dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE,
ADS076RE, ADS067RE, and ADS077RE.
Suitable phosphors for use in phosphor composition 22 include, but
are not limited to: ((Sr.sub.1-z(Ca, Ba, Mg,
Zn).sub.z).sub.1-(x+w)(Li, Na, K,
Rb).sub.wCe.sub.x).sub.3(Al.sub.1-ySi.sub.y)O.sub.4+y+3(x-w)F.sub.1-y--
3(x-w), 0<x.ltoreq.0.10, 0.ltoreq.y.ltoreq.0.5,
0.ltoreq.z.ltoreq.0.5, 0.ltoreq.w.ltoreq.x;
(Ca,Ce).sub.3Sc.sub.2Si.sub.3O.sub.12 (CaSiG);
(Sr,Ca,Ba).sub.3Al.sub.1-xSi.sub.xO.sub.4+xF.sub.1-x:Ce.sup.3+
(SASOF));
(Ba,Sr,Ca).sub.5(PO.sub.4).sub.3(Cl,F,Br,OH):Eu.sup.2+,Mn.sup.2+;
(Ba,Sr,Ca)BPO.sub.5:Eu.sup.2+,Mn.sup.2+;
(Sr,Ca).sub.10(PO.sub.4).sub.6*.nu.B.sub.2O.sub.3:Eu.sup.2+
(wherein 0.ltoreq..nu..ltoreq.1);
Sr.sub.2Si.sub.3O.sub.8*2SrCl.sub.2:Eu.sup.2+;
(Ca,Sr,Ba).sub.3MgSi.sub.2O.sub.8:Eu.sup.2+,Mn.sup.2+;
BaAl.sub.8O.sub.13:Eu.sup.2+;
2SrO*0.84P.sub.2O.sub.5*0.16B.sub.2O.sub.3:Eu.sup.2+;
(Ba,Sr,Ca)MgAl.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+;
(Ba,Sr,Ca)Al.sub.2O.sub.4:Eu.sup.2+;
(Y,Gd,Lu,Sc,La)BO.sub.3:Ce.sup.3+,Tb.sup.3+; ZnS:Cu.sup.+,Cl.sup.-;
ZnS:Cu.sup.+,Al.sup.3+; ZnS:Ag.sup.+,Cl.sup.-;
ZnS:Ag.sup.+,Al.sup.3+;
(Ba,Sr,Ca).sub.2Si.sub.1-.xi.O.sub.4-2.xi.:Eu.sup.2+ (wherein
0.ltoreq..xi..ltoreq.0.2);
(Ba,Sr,Ca).sub.2(Mg,Zn)Si.sub.2O.sub.7:Eu.sup.2+;
(Sr,Ca,Ba)(Al,Ga,In).sub.2S.sub.4:Eu.sup.2+;
(Y,Gd,Tb,La,Sm,Pr,Lu).sub.3(Al,Ga).sub.5-.alpha.O.sub.12-3/2.alpha.:Ce.su-
p.3+ (wherein 0.ltoreq..alpha..ltoreq.0.5);
(Ca,Sr).sub.8(Mg,Zn)(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+,Mn.sup.2+;
Na.sub.2Gd.sub.2B.sub.2O.sub.7:Ce.sup.3+,Tb.sup.3+;
(Sr,Ca,Ba,Mg,Zn).sub.2P.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+;
(Gd,Y,Lu,La).sub.2O.sub.3:Eu.sup.3+, Bi.sup.3+;
(Gd,Y,Lu,La).sub.2O.sub.2S:Eu.sup.3+,Bi.sup.3+;
(Gd,Y,Lu,La)VO.sub.4:Eu.sup.3+,Bi.sup.3+;
(Ca,Sr)S:Eu.sup.2+,Ce.sup.3+; SrY.sub.2S.sub.4:Eu.sup.2+;
CaLa.sub.2S.sub.4: Ce.sup.3+;
(Ba,Sr,Ca)MgP.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+;
(Y,Lu).sub.2WO.sub.6:Eu.sup.3+, Mo.sup.6+;
(Ba,Sr,Ca).sub..beta.Si.sub..gamma.N.sub..mu.:Eu.sup.2+ (wherein
2.beta.3+4.gamma.=3.mu.); Ca.sub.3(SiO.sub.4)Cl.sub.2:Eu.sup.2+;
(Lu,Sc,Y,Tb).sub.2-u-vCe.sub.vCa.sub.1+uLi.sub.wMg.sub.2-wP.sub.w(Si,Ge).-
sub.3-wO.sub.12-u/2 (where -0.5.ltoreq.u.ltoreq.1,
0<v.ltoreq.0.1, and 0.ltoreq.w.ltoreq.0.2);
(Y,Lu,Gd).sub.2-.phi.Ca.sub..phi.Si.sub.4N.sub.6+.phi.C.sub.1-.phi.:Ce.su-
p.3+, (wherein 0.ltoreq..quadrature..ltoreq.0.5); (Lu,Ca,Li,Mg,Y),
.alpha.-SiAION doped with Eu.sup.2+ and/or Ce.sup.3+;
(Ca,Sr,Ba)SiO.sub.2N.sub.2:Eu.sup.2+,Ce.sup.3+;
.beta.-SiAlON:Eu.sup.2+, 3.5MgO*0.5MgF.sub.2*GeO.sub.2:Mn.sup.4+;
Ca.sub.1-c-fCe.sub.cEu.sub.fAl.sub.1+cSi.sub.1-cN.sub.3, (where
0.ltoreq.c.ltoreq.0.2, 0.ltoreq.f.ltoreq.0.2);
Ca.sub.1-h-rCe.sub.hEu.sub.rAl.sub.1-h(Mg,Zn).sub.hSiN.sub.3,
(where 0.ltoreq.h.ltoreq.0.2, 0.ltoreq.r.ltoreq.0.2);
Ca.sub.1-2s-tCe.sub.s(Li,Na).sub.sEu.sub.tAlSiN.sub.3, (where
0.ltoreq.s.ltoreq.0.2, 0.ltoreq.t.ltoreq.0.2, s+t>0); and
(Sr,Ca)AlSiN.sub.3:Eu.sup.2+,Ce.sup.3+.
Phosphor composition 22 may additionally or alternatively include
quantum dot (QD) phosphors or QD materials that emit in any color.
In particular, QD materials for use in phosphor composition 22
include at least one population of QDs capable of emitting green
light upon excitation by a blue light source. The QD wavelengths
and concentrations can be adjusted to meet the optical performance
required. Preferred QD characteristics include high quantum
efficiency (e.g., about 90% or greater), continuous and tunable
emission spectrum, and narrow and sharp spectral emission, e.g.,
less than 50 nm, 30 nm or less, or 20 nm or less full width at half
max (FWHM).
The quantum dot material may include a group II-VI compound, a
group III V compound, a group IV-IV compound, a group IV compound,
a group I-III-VI.sub.2 compound or a mixture thereof. Non-limiting
examples of group II-VI compounds include CdSe, CdTe, CdS, ZnSe,
ZnTe, ZnS, HgTe, HgS, HgSe, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe,
HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe,
HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS,
CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or combinations
thereof. Group III-V compounds may be selected from the group
consisting of GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP, InAs, GaNP,
GaNAs, GaPAs, AlNP, AlNAs, AlPAs, InNP, InNAs, InPAs, GaAlNP,
GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP, InAlNAs,
InAlPAs, and combinations therof. Examples of group IV compounds
include Si, Ge, SiC, and SiGe. Examples of group I-III-VI.sub.2
chalcopyrite-type compounds include CuInS.sub.2, CuInSe.sub.2,
CuGaS.sub.2, CuGaSe.sub.2, AgInS.sub.2, AgInSe.sub.2, AgGaS.sub.2,
AgGaSe.sub.2 and combinations thereof.
QDs for use in phosphor composition 22 may be a core/shell QD,
including a core, at least one shell coated on the core, and an
outer coating including one or more ligands, preferably organic
polymeric ligands. Exemplary materials for preparing core-shell QDs
include, but are not limited to, Si, Ge, Sn, Se, Te, B, C
(including diamond), P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs, AlSb,
GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb,
GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn,
CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, MnS, MnSe, GeS,
GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr,
CuI, Si.sub.3N.sub.4, Ge.sub.3N.sub.4, Al.sub.2O.sub.3, (Al, Ga,
In).sub.2 (S, Se, Te).sub.3, Al.sub.2CO, and appropriate
combinations of two or more such materials. Exemplary core-shell
QDs include, but are not limited to, CdSe/ZnS, CdSe/CdS,
CdSe/CdS/ZnS, CdSeZn/CdS/ZnS, CdSeZn/ZnS, InP/ZnS, PbSe/PbS,
PbSe/PbS, CdTe/CdS and CdTe/ZnS.
The QD materials typically include ligands conjugated to,
cooperated with, associated with, or attached to their surface. In
particular, the QDs may include a coating layer comprising ligands
to protect the QDs from environmental conditions including elevated
temperatures, high intensity light, external gasses, and moisture,
control aggregation, and allow for dispersion of the QDs in the
matrix material.
The ratio of each of the individual phosphors in the phosphor blend
may vary depending on the characteristics of the desired light
output. The relative proportions of the individual phosphors in the
various embodiment phosphor blends may be adjusted such that when
their emissions are blended and employed in an LED lighting device,
there is produced visible light of predetermined x and y values on
the CIE chromaticity diagram. As stated, a white light is
preferably produced. This white light may, for instance, may
possess an x value in the range of about 0.20 to about 0.55, and a
y value in the range of about 0.20 to about 0.55. As stated,
however, the exact identity and amounts of each phosphor in the
phosphor composition can be varied according to the needs of the
end user. For example, the material can be used for LEDs intended
for liquid crystal display (LCD) backlighting. In this application,
the LED color point would be appropriately tuned based upon the
desired white, red, green, and blue colors after passing through an
LCD/color filter combination.
LED devices incorporating the color stable phosphors and used for
backlighting or general illumination lighting may have a color
shift of <1.5 MacAdam ellipses over 2,000 hours of device
operation, and, in particular embodiments, <1 MacAdam ellipse
over 2,000 hours, where the phosphor/polymer composite is in direct
contact with the LED chip surface, LED wall plug efficiency greater
than 40%, and LED current densities are greater than 2 A/cm.sup.2.
In accelerated testing, where the phosphor/polymer composite is in
direct contact with the LED chip surface, LED wall plug efficiency
greater than 18%, and LED current densities are greater than 70
A/cm.sup.2, LED devices may have color shift of <1.5 MacAdam
ellipse over 30 minutes.
The color stable Mn.sup.4+ doped phosphors of the present invention
may be used in applications other than those described above. For
example, the material may be used as a phosphor in a fluorescent
lamp, in a cathode ray tube, in a plasma display device or in a
liquid crystal display (LCD). The material may also be used as a
scintillator in an electromagnetic calorimeter, in a gamma ray
camera, in a computed tomography scanner or in a laser. These uses
are merely exemplary and intended to be not limiting.
EXAMPLES
Comparative Examples 1-2
A treatment solution composed of K.sub.2SiF.sub.6 dissolved in 49%
HF was prepared by adding 4.2 g K.sub.2SiF.sub.6 per 100 ml 49% HF
to form a suspension which was vacuum filtered to remove excess
solids. Approximately 2 vol % 49% HF was added to the saturated
solution, to form a nearly saturated solution.
Samples of Mn-doped potassium fluorosilicate phosphor,
K.sub.2SiF.sub.6:Mn were added to separate treatment solution at a
rate of about 6 ml solution per 1 g product and stirred for about
20 minutes. The treated product was vacuum filtered, rinsed once
with acetic acid and three times with acetone, and then dried under
vacuum. The dried powder was sifted through a 170-mesh screen, and
annealed under an atmosphere composed of 20% F.sub.2/80% nitrogen
for about 8 hours at 540.degree. C.
The annealed phosphor was mixed with treatment solution of 49% HF
nearly saturated with K.sub.2SiF.sub.6 at a rate of about 12 ml
solution per 1 g product and stirred for about 20 minutes. The
treated product was vacuum filtered, rinsed once with acetic acid
and three times with acetone, and then dried under vacuum. The
dried powder was sifted through a 170-mesh screen.
Examples 1 and 2
The treated phosphors of Comparative Examples 1 and 2 were placed
in a container composed of a fluoropolymer and annealed at
90.degree. C. for 8 hours under a 20% F.sub.2/80% nitrogen
atmosphere.
Tapped bulk density of the phosphors of Examples 1 and 2 and
Comparative Examples 1 and 2 was determined by tapping a vessel
containing the phosphor and measuring the volume of the powder.
Particle size data was obtained using a Horiba LA-960 Laser
Scattering Particle Size Distribution Analyzer. Tapped bulk density
data, quantum efficiency, lifetime, and particle size distribution
for the products is shown in Table 1.
TABLE-US-00001 bulk % Rel d10/d50/d90 density density QE, particle
size, Example no. sample ID (g/mL) decrease % Lifetime (ms) .mu.m
Comparative Ex. 1 C072215A- 0.75 6.4% 103.7 8.449 17/28/47
TGAT(133) Example 1 C072215A- 0.70 103.8 8.45 16/28/49 TGATA(134)
Comparative Ex. 2 C072215B- 0.77 6.5% 103 8.454 15/24/37 TGAT(133)
Example 2 C072215B- 0.72 103.1 8.445 14/22/33 TGATA(134)
It can be seen that the phosphors of Examples 1 and 2 had lower
bulk density relative to those of Comparative Examples 1 and 2,
while other properties remain constant. The drop in bulk density
may be due to less agglomeration of the particles which may result
in improved device performance.
While only certain features of the invention have been illustrated
and described herein, many modifications and changes will occur to
those skilled in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes as fall within the true spirit of the invention.
* * * * *